Various flocculants including polymeric flocculants have been used in order to flocculate and dewater sludge generated from municipal sewage and industrial wastewater. A method for flocculating and precipitating solid contents by adding a polymer flocculant to waste water has been widely adopted. In these methods, a process of adding a dilute aqueous solution of the polymer flocculant to waste water or sludge is typical. Flocculants are added to facilitate the settling of suspended particles in a solution. Flocculants facilitate the agglomeration and, therefore, make larger floccules. These tend to settle down due to gravitational force. Flocculants try to bridge the molecules forming clumps. For example, an anionic flocculant will react with a positively charge polymer and will adsorb those particles.
In recent years, sludge generated from municipal sewage and industrial wastewater has been increasing because of changes in the recent living environment. Furthermore, the properties of the sludge are becoming worse. Due to increasing demand of cationic polymer flocculants in these application there is a need to develop new cationic block copolymers designed for cost-effective solids/liquid separation processes.
In addition to the use as polymeric flocculants, water-soluble polymers, in particular, high-molecular weight water-soluble polymers are used in various technical fields such as retention aids, paper strength agents, and thickeners.
Such water-soluble polymers include homopolymers prepared by polymerizing an anionic monomer such as an acrylate or a methacrylate, a cationic monomer such as dimethylaminoethyl(meth)acrylate quaternary salt, or a nonionic monomer such as (meth)acrylamide and also include ionic polymers such as copolymers of an anionic monomer and a nonionic monomer; copolymers of a cationic monomer and a nonionic monomer; and copolymers of a cationic monomer, an anionic monomer, and a nonionic monomer.
Conventionally, a cationic polymer flocculant is used for dewatering sewage sludge and the like, and also as a retention aid in paper making. On the market there exists quite a broad range of polyacrylamide flocculants used in the water treatment and as sludge dewatering polymers. However, the known flocculants consisting of acrylamide-cationic monomers based copolymers have limited performance at high pH due to low resistance to hydrolysis and low stability under high shear conditions.
With traditional polyacrylamide flocculants, under certain circumstances (high pH value), the amide group present in the polymer backbone can react with their neighboring cationic ester groups. A cationic copolymer is then transformed to a non-ionic or even anionic copolymer with inexistent or poor dewatering activities. Therefore there is a need to find more stable acrylamide-based copolymers.
The cationic polymers are also widely used in the paper industry. They are often referred to as fixatives, drainage aids, and/or retention aids, and they are added to the pulp before or during paper production. The term “fixing” generally implies the binding of small particles to pulp fibers. Fixatives build up agglomerates with colloidal material in the water phase and attach them onto fibers so that they end up in the final paper sheet. It is known that the existing cationic polymers do not work well under all circumstances. Therefore there is a constant need to find better performing polymers for use in the paper making processes or at least find new alternatives for the existing ones.